We have established methodology for measuring plasma, urine, tissue, and cerebrospinal fluid levels of the catecholamine precursor dihydroxyphenylalanine (DOPA), the catecholamines norepinephrine (NE), epinephrine (E), and dopamine (DA), and the deaminated catecholamine metabolites dihydroxyphenylglycol (DHPG) and dihydroxyphenylacetic acid (DOPAC) simultaneously using liquid chromatography with electrochemical detection (LCED). We also have developed radioimmunoassay methodology for measuring specifically the 1-28 form of human ANP and measuring angiotensin II (AII) using liquid chromatography with radioimmunoassay (LC/RIA). Plasma DOPA derives extensively from sympathetic nerve endings and may indicate activity of the rate-limiting step in catecholamine biosynthesis. Simultaneous measurement of DHPG and NE provides more information about noradrenergic function than measuring either substance alone. Immunoreactive ANP increases with salt loading and decreases with standing upright, and there is an arteriovenous decrement in immunoreactive ANP in the human arm.